Solid-state imaging element and camera system

ABSTRACT

A solid-state imaging element that includes a plurality of semiconductor layers stacked, a plurality of stack-connecting parts for electrically connecting the plurality of semiconductor layers, a pixel array part in which pixel cells that include a photoelectric conversion part and a signal output part are arrayed in a two-dimensional shape, and an output signal line through which signals from the signal output part of the pixel cells are propagated, in which the plurality of semiconductor layers includes at least a first semiconductor layer and a second semiconductor layer, and, in the first semiconductor layer, the plurality of pixel cells are arrayed in a two-dimensional shape, the signal output part of a pixel group formed with the plurality of pixel cells shares an output signal line wired from the stack-connecting parts, and the output signal line has a separation part which can separate each output signal line.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.13/218,979 filed Aug. 26, 2011, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication No. JP 2010-197734 filed on Sep. 3, 2010 in the Japan PatentOffice, the entirety of which is incorporated by reference herein to theextent permitted by law.

BACKGROUND

The present technology relates to a solid-state imaging elementrepresented by a CMOS image sensor and a camera system.

A solid-state imaging element is configured to have a photoelectricconversion unit, a charge voltage conversion unit which convertsaccumulated charges into a voltage, and a unit pixel with an amplifyingcircuit for reading the voltage of the charge voltage conversion unit.

There has been a proposed technology with regard to such a solid-stateimaging element in which the opposite side (=back face) of a face wheretransistors are arranged is set to a light-irradiated face, and aplurality of semiconductor layers is stacked to read an output signal ofpixels, thereby improving the degree of integration and parallelism.

The technology is disclosed in, for example, Japanese Unexamined PatentApplication Publication No. 2006-049361.

FIG. 1 is a diagram showing a basic configuration of a solid-stateimaging element disclosed in Japanese Unexamined Patent ApplicationPublication No. 2006-049361.

In FIG. 1, pixel cells 2 are arranged in an array shape on a firstsemiconductor layer 1-1 in the light sensing part side, row scanningcircuits 3-1 and 3-2 are arranged in both sides of the array part, andpixel driving circuits 4-1 and 4-2 are arranged corresponding to therows of the pixel cells 2.

FIG. 2 is a diagram showing an example of a pixel of a CMOS image sensorwhich includes four transistors.

The pixel cells 2 include a photoelectric conversion unit (photoelectricconversion element) 21 composed of, for example, a photodiode (PD).

In addition, the pixel cells 2 include four transistors including atransfer transistor 22, a reset transistor 23, an amplifying transistor24, and a selection transistor 25 for the one photoelectric conversionunit 21 as active elements.

The photoelectric conversion unit 21 performs photoelectric conversionof incident light into charges (herein, electrons) in an amountcorresponding to the quantity of the light.

The transfer transistor 22 is connected between the photoelectricconversion unit 21 and a floating diffusion FD as an output node, andthe gate thereof (transfer gate) is given a transfer signal TRG that isa control signal through a transfer control line LTRG.

Accordingly, the transfer transistor 22 transfers the electronsphotoelectrically converted in the photoelectric conversion unit 21 tothe floating diffusion FD.

The reset transistor 23 is connected between a power supply line LVDDand the floating diffusion FD, and the gate thereof is given a resetsignal RST that is a control signal through a reset control line LRST.

Accordingly, the reset transistor 23 resets the potential of thefloating diffusion FD to the potential of the power supply line LVDD.

The gate of the amplifying transistor 24 is connected to the floatingdiffusion FD. The amplifying transistor 24 is connected to an outputsignal line 6 through the selection transistor 25, and constitutes asource follower as a constant current source outside the pixel part.

The amplifying transistor 24 and the selection transistor 25 form anamplifying circuit 7.

In addition, a selection signal SEL that is a control signal is given tothe gate of the selection transistor 25 through a selection control lineLSEL according to an address signal to turn on the selection transistor25.

If the selection transistor 25 is turned on, the amplifying transistor24 amplifies the potential of the floating diffusion FD and outputs avoltage according to the potential to the output signal line 6.

FIG. 3 is a diagram showing an example of pixel sharing of a COMS imagesensor.

In this configuration, four pixel cells 2-1 to 2-4 having each ofphotoelectric conversion elements 21-1 to 21-4 and transfer transistors22-1 to 22-4 share the floating diffusion FD, the reset transistor 23,and the amplifying circuit 7.

In the solid-state imaging element, the pixel cells of FIG. 2 that haveone amplifying circuit 7 for one photoelectric conversion unit 21 formedon the first semiconductor layer 1-1, the pixel cells of FIG. 3 thathave one amplifying circuit 7 for a plurality of photoelectricconversion units 21, or the like is applied as shown in FIG. 1.

In addition, the solid-state imaging element in Japanese UnexaminedPatent Application Publication No. 2006-049361 has a structure in whichstack-connecting terminals (micro-bumps or through holes VIA) 8 thatpropagate signals to a different stacked second semiconductor layer 1-2are connected in the pixel cells 2.

In other words, each of the stack-connecting terminals 8 is connected tothe amplifying circuit 7 that reads signals.

In the examples of FIGS. 2 and 3, a bias transistor (load MOS) 9 thatfunctions as a constant current source of a source follower is formed onthe second semiconductor layer 1-2.

SUMMARY

When the size of a unit pixel is smaller than the size of thestack-connecting terminal 8, it is difficult to arrange thestack-connecting terminals 8 for each of unit pixels in any event in theabove-described related art.

For this reason, it is considered that the output of the amplifyingcircuits of a plurality of pixel cells shares an output signal lineconnected to the stack-connecting terminals as shown in FIG. 4.

FIG. 5 is a diagram showing an example of principal circuits of thesolid-state imaging element of FIG. 4.

In this example, output terminals of the amplifying circuits 7 readingthe plurality of pixel cells are connected to the same output signalline 6, and the connection node thereof is connected to the secondsemiconductor layer 1-2 through the stack-connecting terminal 8.

The pixel cells 2 include a plurality of photoelectric conversion units(PD) as shown in FIG. 2, and it does not matter to share the amplifyingcircuit 7.

As described above, the amplifying circuit 7 includes the selectiontransistor 25 in addition to the amplifying transistor 24, and isconnected to the output signal line 6 through the selection transistor25.

However, it is possible to omit the selection transistor 25 by settingthe voltage of the FD in a non-selected pixel to be low using the resettransistor 23 and by driving the amplifying transistor 24 to be in anOFF state.

In the configuration of FIGS. 4 and 5, when a pixel is selected by therow scanning circuit 3 and signals are output through thestack-connecting terminal 8, it is necessary to drive parasiticcapacitance of the output terminal of the amplifying circuit 7 of otherpixels connected to the same stack-connecting terminal 8.

In other words, parasitic capacitance of a source terminal of theamplifying transistor 24, parasitic capacitance of a source terminal ofthe selection transistor 25, or parasitic capacitance of wiring is addedas load capacity.

With an increase in the parasitic capacitance of the output signal line6 including the stack-connecting terminal 8, the time necessary forconverging an output signal after the selection of a pixel on a targetvalue is lengthened, thereby obstructing speed-up.

When it is necessary to perform a further speedy reading operation,elevating a current flowing into the amplifying circuit 7 by changing,for example, a bias voltage Vb applied to the gate of the biastransistor 9 is considered, but an increase in power consumption resultsin proportion to increments of the current.

It is desirable for the technology to provide a solid-state imagingelement and a camera system which enable the realization of speedincreases in driving an output signal line of a pixel and low powerconsumption in a stacking structure.

According to an embodiment of the present technology, there is provideda solid-state imaging element which includes a plurality ofsemiconductor layers stacked, a plurality of stack-connecting parts forelectrically connecting the plurality of semiconductor layers, a pixelarray part in which pixel cells that include a photoelectric conversionpart and a signal output part are arrayed in a two-dimensional shape,and an output signal line through which signals from the signal outputpart of the pixel cells are propagated, and in which the plurality ofsemiconductor layers includes at least a first semiconductor layer and asecond semiconductor layer, and, in the first semiconductor layer, theplurality of pixel cells are arrayed in a two-dimensional shape, thesignal output part of a pixel group formed with the plurality of pixelcells shares an output signal line which is wired from thestack-connecting part, and the output signal line has a separation partwhich can separate each output signal line that is arbitrarily branchedat all or some locations branched from the stack-connecting part.

According to another embodiment of the technology, there is provided acamera system which includes a solid-state imaging element, an opticalsystem which forms an image of a subject on the imaging element, and asignal processing circuit which processes an output image signal of theimaging element, and in which the solid-state imaging element includes aplurality of semiconductor layers stacked, a plurality ofstack-connecting parts for electrically connecting the plurality ofsemiconductor layers, a pixel array part in which pixel cells that havea photoelectric conversion part and a signal output part are arrayed ina two-dimensional shape, and an output signal line through which signalsby the signal output part of the pixel cells are propagated, theplurality of semiconductor layers includes at least a firstsemiconductor layer and a second semiconductor layer, and, in the firstsemiconductor layer, the plurality of pixel cells is arrayed in atwo-dimensional shape, a signal output part of a pixel group formed withthe plurality of pixel cells shares the output signal line wired fromthe stack-connecting parts, and the output signal line has a separationpart which can separate each output signal line that is arbitrarilybranched at all or some locations branched from the stack-connectingparts.

According to the technology, it is possible to realize speed-up indriving the output signal line in a pixel in a stacking structure andlow power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a basic configuration of a solid-stateimaging element disclosed in Japanese Unexamined Patent ApplicationPublication No. 2006-049361;

FIG. 2 is a diagram showing an example of a pixel of a CMOS image sensorincluding four transistors;

FIG. 3 is a diagram showing an example of pixel sharing of a CMOS imagesensor;

FIG. 4 is a diagram showing a configuration example of a solid-stateimaging element in which the output of amplifying circuits of aplurality of pixel cells shares an output signal line connected tostack-connecting terminals;

FIG. 5 is a diagram showing an example of principal circuits of thesolid-state imaging element of FIG. 4;

FIG. 6 is a diagram showing a configuration example of a CMOS imagesensor (solid-state imaging element) according to an embodiment of thepresent technology;

FIG. 7 is a diagram showing an example of a pixel of the CMOS imagesensor including four transistors according to the embodiment;

FIG. 8 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts in a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a first embodiment of the technology;

FIG. 9 is a diagram showing an example of principal circuits of the CMOSimage sensor (solid-state imaging element) of FIG. 8;

FIG. 10 is a diagram showing an example of principal circuits of a CMOSimage sensor (solid-state imaging element) according to a secondembodiment of the technology;

FIG. 11 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts in a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a third embodiment of the technology;

FIG. 12 is a diagram showing an example of principal circuits of a CMOSimage sensor (solid-state imaging element) according of FIG. 11;

FIG. 13 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts in a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a fourth embodiment of the technology;

FIGS. 14A to 14D-3 are diagrams illustrating an arrangement example ofthe pixels, the stack-connecting terminals, and the separation parts indetail according to the fourth embodiment;

FIGS. 15A and 15B are diagrams showing examples in which the elementsare arranged so that switches and dummy transistors of the separationparts at branch points hold periodicity;

FIG. 16 is a diagram showing an example in which the elements arearranged so that switches and dummy transistors of the separations partat branch points hold periodicity, and the dummy transistors have apredetermined function;

FIG. 17 is a diagram showing a layout example when a stack-connectingterminal is shared in 4×4 pixel cells;

FIG. 18 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a fifth embodiment ofthe technology;

FIG. 19 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a sixth embodiment ofthe technology;

FIG. 20 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a seventh embodimentof the technology;

FIG. 21 is a diagram showing a stacking structure example of a firstsemiconductor layer, a second semiconductor layer, and a thirdsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a eighth embodiment of the technology;

FIG. 22 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a ninth embodiment ofthe technology; and

FIG. 23 is a diagram showing an example of a configuration of a camerasystem to which the solid-state imaging elements according to theembodiments of the technology are applied.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the technology will be described in relationto drawings.

Description will be provided in the following order.

1. Example of Overall Configuration of Solid-state Imaging Element

2. Basic Concept of Characteristic Configuration for Adopting StackingStructure

3. First Embodiment

4. Second Embodiment

5. Third Embodiment

6. Fourth Embodiment

7. Fifth Embodiment

8. Sixth Embodiment

9. Seventh Embodiment

10. Eighth Embodiment

11. Ninth Embodiment

12. Tenth Embodiment (Configuration Example of Camera System)

1. Example of Overall Configuration of Solid-State Imaging Element

FIG. 6 is a diagram showing a configuration example of a CMOS imagesensor (solid-state imaging element) according to an embodiment of thetechnology.

The CMOS image sensor 100 includes a pixel array part 110, a rowselection circuit (Vdec) 120 as a pixel driving unit, and a readoutcircuit (AFE) 130.

In the present embodiment, the opposite side (=rear face) of a face onwhich transistors are arranged is set to a light-irradiated face as anexample, and a plurality of semiconductor layers are stacked and formedso as to read output signals of pixels.

A characteristic configuration corresponding to a stacking structure ofthe semiconductor layer will be described later.

The pixel array part 110 is arranged with a plurality of pixel cells110A in a two-dimensional shape (matrix shape) with M rows×N columns.

FIG. 7 is a diagram showing an example of a pixel of the CMOS imagesensor including four transistors according to the embodiment.

The pixel cell 110A includes a photoelectric conversion unit(photoelectric conversion element) 111 including, for example, aphotodiode (PD).

In addition, the pixel cell 110A has four transistors including atransfer transistor 112, a reset transistor 113, an amplifyingtransistor 114, and a selection transistor 115 as active elements forthe one photoelectric conversion unit 111.

The photoelectric conversion unit 111 performs photoelectric conversionfor incident light into charges (herein, electrons) in an amountcorresponding to the quantity of the light.

The transfer transistor 112 is connected between the photoelectricconversion unit 111 and a floating diffusion FD as an output node, andthe gate thereof (transfer gate) is given a transfer signal TRG that isa control signal through a transfer control line LTRG.

Accordingly, the transfer transistor 112 transfers the electronsphotoelectrically converted in the photoelectric conversion unit 111 tothe floating diffusion FD.

The reset transistor 113 is connected between a power supply line LVREFand the floating diffusion FD, and the gate thereof is given a resetsignal RST that is a control signal through a reset control line LRST.

Accordingly, the reset transistor 113 resets the potential of thefloating diffusion FD to the potential of the power supply line LVREF.

The floating diffusion FD is connected to the gate of the amplifyingtransistor 114. The amplifying transistor 114 is connected to an outputsignal line 116 through the selection transistor 115, and constitutes asource follower as a constant current source outside the pixel part.

An amplifying circuit 117 is formed with the amplifying transistor 114and the selection transistor 115 as a signal output part.

In addition, a selection signal SEL that is a control signalcorresponding to an address signal is given to the gate of the selectiontransistor 115 through a selection control line LSEL to turn on theselection transistor 115.

If the selection transistor 115 is turned on, the amplifying transistor114 amplifies the potential of the floating diffusion FD and outputs avoltage corresponding to the potential to the output signal line 116.

The voltage output from each pixel is output to a readout circuit 130through the output signal line 116.

These operations are simultaneously performed for pixels of one rowbecause, for example, the gates of the transfer transistor 112, thereset transistor 113, and the selection transistor 115 are connected toone another in a row unit.

As described above, the amplifying circuit 117 includes the selectiontransistor 115 in addition to the amplifying transistor 114, and isconnected to the output signal line 116 via the selection transistor115.

However, it is possible to omit the selection transistor 115 by settingthe voltage of the FD of a non-selected pixel to be low by the resettransistor 113 and driving the amplifying transistor 114 to be off.

The reset control line LRST, the transfer control line LTRG, and theselection control line LSEL wired in the pixel array part 110 are wiredin a row unit of the pixel array.

The reset control line LRST, the transfer control line LTRG, and theselection control line LSEL are driven by the row selection circuit 120.

The row selection circuit 120 controls an operation of a pixel arrangedin an arbitrary row in the pixel array part 110. The row selectioncircuit 120 functions as a pixel driving unit which controls the drivingof a pixel through the control lines LSEL, LRST, and LTRG.

The readout circuit 130 performs a predetermined process for a signalVSL output through the output signal line 116 from each pixel cell 110Ain a read row that is selected or pre-selected by driving of the rowselection circuit 120, and temporarily retains a pixel signal that is,for example, subjected to a signal processing.

The readout circuit 130 is applicable to a configuration of a circuitincluding a sample-and-hold circuit that performs sampling and holdingfor a signal output through the output signal line 116.

Alternatively, the readout circuit 130 includes a sample-and-holdcircuit, and is applicable to a configuration of a circuit with afunction of removing a reset noise and a fixed-pattern noise specifiedfor a pixel such as unevenness in threshold values of the amplifyingtransistor 114 by a CDS (Correlated Double Sampling) process.

In addition, the readout circuit 130 is equipped with an analog anddigital (AD) converting function, and is applicable to a configurationin which a signal level is set to a digital signal.

Hereinafter, a characteristic configuration corresponding to thestacking structure of a semiconductor layer in the CMOS image sensor 100according to the embodiment will be described in detail.

2. Basic Concept of Characteristic Configuration for Adopting StackingStructure

First, the basic concept of a characteristic configuration for adoptingthe stacking structure will be described.

In the CMOS image sensor (solid-state imaging element) 100, basically, aplurality of stacked semiconductor layers is electrically connected toone another with a plurality of stack-connecting terminals(stack-connecting part).

The photoelectric conversion unit 111 and unit pixel cells 110A havingsignal output parts are two-dimensionally arrayed on a firstsemiconductor layer.

The signal output parts of a pixel group including a plurality of pixelcells share the output signal line 116 wired from the stack-connectingterminal.

In addition, the output signal line 116 has a separation part which canseparate each output signal line 116 that is arbitrarily branched in allor some of the locations branched from the stack-connecting terminal.

More specifically, an output of the amplifying circuit 117 that includesa plurality of amplifying transistors is connected to thestack-connecting terminal, and some or all of branch points betweenstack-connecting terminals and the amplifying circuits 117 have aseparation part which separates the output signal line 116.

The CMOS image sensor (solid-state imaging element) 100 has alight-irradiated face, for example, at the opposite side of the facewhere transistors and wires are arranged.

In the CMOS image sensor 100, when an output signal is propagated to thefirst semiconductor layer and a different semiconductor layer that arestacked through stack-connecting terminals, the degree of freedom forarranging the stack-connecting terminals rises, and transistors can beadditionally arranged within a pixel array in small numbers withoutdownscaling the photoelectric conversion unit.

By making use of the above advantage, it is possible to reduce theactual load capacity when reading signals of pixels through theamplifying circuit 117, with a separation part such as a switch forseparating each branch wiring at a node at which wiring from astack-connecting terminal to each unit pixel is branched.

In the embodiment, a stack-connecting terminal is characteristic in thatthe terminal is arranged in the vicinity of the center of the pixelgroup connected thereto.

Furthermore, the stack-connecting terminal can evenly divide parasiticcapacitance of each wiring separated at a separation part by beingarranged in the vicinity of the center of the pixel group connectedthereto in the range of intervals in which stack-connecting terminalscan be satisfactorily arranged.

Accordingly, it is possible to minimize the actual load capacity whenreading signals of each pixel through the amplifying circuit 117.

In the embodiment, the branch point is characteristic in that the branchpoint is arranged in the vicinity of the center of the pixel group whichis connected after the branch point.

Furthermore, the branch point can evenly divide parasitic capacitance ofeach wiring separated at the separation part by arranging the branchpoint in the vicinity of the center of the pixel group which isconnected after the branch point.

Accordingly, it is possible to minimize the actual load capacity whenreading signals of each pixel through the amplifying circuit 117.

In the embodiment, the separation part arranged in the branch point ischaracteristic in that an element same as the separation part isdummy-arranged in an area where a separation part is not arranged so asto have periodicity in arrangement.

Accordingly, it is possible to have periodicity of the layout of pixelsand circuits, to have uniform imaging characteristics and operationcharacteristics of transistors, and to avoid image deterioration such asfixed-pattern noise, or the like.

In the embodiment, the pixel group that is two-dimensionally arrayed isconnected to the same stack-connecting terminal.

By connecting the two-dimensionally arrayed pixel group to the samestack-connecting terminal, not only in the row or column direction, itis possible to minimize the distance from a stack-connecting terminal tothe furthest pixel even when the number of pixels connected to thestack-connecting terminal is the same.

Accordingly, in the embodiment, it is possible to make voltage dropsuniform in readout voltages by parasitic resistance for each pixel.

As a general readout circuit of output signals of pixels, the amplifyingtransistor 114 in a pixel, and the source follower circuit including aconstant current source by the bias transistor connected to the outputsignal line 116 can be exemplified.

Since the parasitic capacitance of the output signal line 116 isdischarged with a constant current, particularly, capacitance componentsare dominant at a convergence time of output, it is possible to attainspeed-up or low power consumption in proportion to the separation of thecapacitance.

On the other hand, since what is dominant is capacitive discharge, not atime constant of the wiring, it is characteristic that the convergencetime does not dominantly deteriorate by resistance components, and thereis almost no overhead incurred by the addition of a switch as aseparation part.

On the other hand, uniformity is regarded as important in the resistancecomponents of the output signal line 116. An input voltage of a sourcefollower circuit is output to a source terminal of the amplifyingtransistor 114.

For this reason, the output voltage in the stack-connecting terminal isoffset by a product of wiring resistance from the amplifying transistor114 to the stack-connecting terminal as an output terminal and aconstant current generated in the load MOS (bias transistor) that is thecurrent source.

The offset voltage can be easily cancelled by a CDS unit such as acorrelated double sampling, but if the voltage differs for each pixel, asufficient margin is necessary for a voltage range that can be input toan analog signal processing circuit such as an analog and digitalconversion circuit after the output terminal.

In the embodiment, since a switch as a separation means in the branchpoint is added to each separated output signal line 116, it ischaracteristic that uniformity of resistance components of the outputsignal line 116 is not impaired.

Next, specific configuration examples will be described.

3. First Embodiment

FIG. 8 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts in a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a first embodiment of the technology.

FIG. 9 is a diagram showing an example of principal circuits of the CMOSimage sensor (solid-state imaging element) of FIG. 8.

In the CMOS image sensor 100A of the first embodiment, pixel cells 110Aare arranged on a first semiconductor layer 200 in an array shape. Rowscanning circuits 121-1 and 121-2 are arranged on the both sides of thepixel array part 110, and pixel driving circuits 122-1 and 122-2 arearranged corresponding to rows of the pixel cells 110A.

In the first embodiment, an amplifying circuit 117 of the pixel cell110A shares the output signal lines 116 in the column direction and isconnected to a stack-connecting terminal 118.

A separation part 140 of the output signal line 116 is provided on alocation where the output signal line 116 branches between thestack-connecting terminal 118 and the amplifying circuit 117 of eachpixel cell.

In the pixel array part 110 of FIG. 8, pixel cells are arranged in a 6×6matrix shape.

In the first embodiment, it is preferable that the stack-connectingterminal 118 may be arranged at the center of a pixel group of aplurality of pixel cells 110A connected thereto in the range of aminimum interval between stack-connecting terminals that can beproduced.

In this case, ideally, it is preferable that the stack-connectingterminals 118 are positioned in between the formation locations of thethird and fourth pixel cells in columns CL0 to CL5, that is, at thecenter of each column, in the pixel array of FIG. 8.

When center arrangement is not possible, it is preferable to arrange thestack-connecting terminals in the vicinity of the center within therange where the terminals can be arranged as shown in FIG. 8.

In FIG. 8, the stack-connecting terminals 118 are arranged in betweenthe formation locations of the fourth and the fifth pixel cells, thatis, in the vicinity of the center within the range where the terminalscan be arranged, in the even columns CL0, CL2, and CL4.

The stack-connecting terminals 118 are arranged in between the formationlocations of the second and the third pixel cells, that is, in thevicinity of the center within the range where the terminals can bearranged, in the odd columns CL1, CL3, and CL5.

In the example of FIGS. 8 and 9, the separation part 140 is arranged soas to be separated in the stacking direction and to overlap thestack-connecting terminal 118.

Furthermore, FIG. 9 includes four pixel cells 110A-1 to 110A-4 forsimplification, and shows an example where the stack-connecting terminal118 and the separation part 140 are arranged substantially at the centerof the pixel group.

As shown in FIG. 9, the separation part 140 at the branch point includesa switch 141, and separates the output signal line 116 into two outputsignal line 116-1 and 116-2.

The output signal line 116-1 is connected to the amplifying circuits 117of the pixel cells 110A-1 and 110A-2 and the output signal line 116-2 isconnected to the amplifying circuits 117 of the pixel cells 110A-3 and110A-4.

The switch 141 that constitutes the separation part 140 includes a pairof terminals a and b and a pair of terminals c and d.

The terminal a is connected to the stack-connecting terminal 118 and theterminal b is connected to the one output signal line 116-1.

The terminal c is connected to the stack-connecting terminal 118 and theterminal d is connected to the other output signal line 116-2.

With the switch 141 of the above configuration, the terminals a and band the terminals c and d are switched to a connection or non-connectionstate according to a switching signal SSW by a control system that isnot shown in the drawing.

The switch 141 can be realized with a sample circuit in which either orboth a NMOS transistor and a PMOS transistor are connected thereto inparallel, or the like.

In the example of FIG. 9, a bias transistor (load MOS) 119 whichfunctions as a constant current source of the source follower is formedon the second semiconductor layer 210.

The bias transistor 119 has a function of inputting a bias voltage Vb toa gate so that a constant current flows from the output signal line 116.

The bias transistor 119 may be arranged in the first semiconductor layer200.

4. Second Embodiment

FIG. 10 is a diagram showing an example of principal circuits of a CMOSimage sensor (solid-state imaging element) according to a secondembodiment.

A point that the CMOS image sensor 100B according to the secondembodiment differs from the CMOS image sensor 100A according to thefirst embodiment is that the number of branches of the output signalline 116 by a separation part 140B is not two but more than that(herein, three branches).

In the CMOS image sensor 100B, the output signal line 116 is branchedinto three output signal lines 116-1, 116-2, and 116-3.

In addition, the amplifying circuits 117 of the pixel cells 110A-5 and110A-6 are connected to the output signal line 116-3.

A switch 141B includes a pair of terminals e and f in addition to theconfiguration of FIG. 9.

In addition, the terminal e is connected to the stack-connectingterminal 118 and the terminal f is connected to the output signal line116-3.

With the switch 141B of the above configuration, the terminals a and b,the terminals c and d, and the terminals e and f are switched to aconnection or non-connection state according to a switching signal SSWby a control system that is not shown in the drawing.

5. Third Embodiment

FIG. 11 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts on a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a third embodiment of the technology.

FIG. 12 is a diagram showing an example of principal circuits of theCMOS image sensor (solid-state imaging element) of FIG. 11.

The CMOS image sensor 100C according to the third embodiment isconfigured to have pixel groups sharing the stack-connecting terminals118, including pixels arranged perpendicular (the horizontal directionin FIG. 11) to the readout scanning direction of pixels (the verticaldirection in FIG. 11).

In the example of FIG. 11, each of two columns of the zeroth and thefirst columns, the second and the third columns, and the fourth and thefifth columns shares one stack-connecting terminal 118.

In addition, an output line L141 which extends from the output of theseparation part 140-1 that is arranged in the middle of theeven-numbered column and an output line L142 wired so as to return tothe even-numbered column side from the output of the separation part140-2 in the odd-numbered column side are connected to the separationpart 140-3 arranged at a first branch point.

The separation parts 140-0 and 140-1 form a second branch point, andbasically have the same configuration as in the first embodiment.

A switch 141-3 constituting the separation part 140-3 at the firstbranch point includes a pair of terminals g and h, and a pair ofterminals i and j.

The terminal g is connected to the stack-connecting terminal 118 and theterminal h is connected to the one output line L141.

The terminal i is connected to the stack-connecting terminal 118 and theterminal j is connected to the other output line L142.

With the switch 141-3 of the above configuration, the terminals g and hand the terminals i and j are switched to a connection or non-connectionstate according to a switching signal SSW by a control system that isnot shown in the drawing.

In the third embodiment, the first separation part 140-3 is positionedat the first branch point that branches first from the stack-connectingterminal 118 and the second separation parts 140-1 and 140-2 arepositioned at the second branch point that branches after that.

A plurality of pixels included in the same pixel group is simultaneouslyselected by readout scanning, but any one of the pixels that issimultaneously selected is connected to the stack-connecting terminal118 by the first or the second separation part.

In the example of FIG. 12, the number of pixel cells connected to thestack-connecting terminal 118 during reading of pixels is reduced to onefourth of a case where a separation part is not provided, whereby it ispossible to speed-up and low power consumption by a decrease inparasitic capacitance.

In the example of FIG. 12, both the first and the second branch pointshave separation parts, but it does not matter that either of the branchpoints has a separation part.

For example, when only the first branch point is provided with aseparation part, it is possible to reduce the total parasiticcapacitance of the output signal line 116 by half.

When a separation part is arranged only at the two second branch points,it is possible to reduce the number of connected pixel cells by onefourth by connecting any one of four switches arranged at the branchpoints.

When parasitic capacitance of wiring from the first branch point to thesecond branch points is sufficiently smaller than the parasiticcapacitance after the second branch points, substantially the sameeffect is obtained even when the separation part 140-3 at the firstbranch point is omitted.

On the contrary, when parasitic capacitance of wiring from the firstbranch point to the second branch points is greater, it is preferable tohave a separation part at the first branch point also.

6. Fourth Embodiment

FIG. 13 is a diagram showing an arrangement example of pixels,stack-connecting terminals, and separation parts on a firstsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to a fourth embodiment of the technology.

FIGS. 14A to 14D-3 are diagrams illustrating an arrangement example ofthe pixels, the stack-connecting terminals, and the separation parts indetail according to the fourth embodiment.

In a pixel array part 110D of FIG. 13, pixel cells are arranged in a 6×6matrix shape.

In addition, FIG. 13 shows an arrangement example when a 4×4 pixel cellgroup GRP shares one stack-connecting terminal 11 as an example.

In order to minimize the length of wiring to the furthest pixel, it ispreferable to arrange the stack-connecting terminal 118 in the vicinityof the center of the 4×4 pixel cell group GRP.

Furthermore, it is preferable to arrange the first branch point at whichthe first separation part 140-3 is arranged in the vicinity of thecenter of the pixel cell group GRP, as shown in FIG. 14A.

Furthermore, as shown in FIG. 14B, the second separation parts 140-1 and140-2 of the second branch point are arranged around of the center ofeach pixel cell group GRP separated by the first branch point.

In the same manner, as shown in FIG. 14C, a third separation part 140-4of a third branch point is arranged around the center of each pixel cellgroup GRP separated by the second branch points 140-1 and 140-2.

As a result, the configuration of the arrangement of the separationparts and the output single lines 116 as shown in FIG. 14D is preferableto minimize wiring capacity or wiring resistance.

However, there is no strict limitation on the center arrangement due tothe degree of complexity in the arrangement and wiring of transistors,but satisfactory effects are obtained if the separation parts arearranged in the vicinity of the center within a viable range.

In addition, as shown in FIG. 14D-2, it is preferable to arrange a dummytransistor DMT as a dummy element at a location where separation meansis not arranged in consideration of periodicity in the arrangement ofthe separation means.

By maintaining periodicity in the formation of transistors of each pixelcell, characteristics of light sensing elements and transistors areuniformed and the occurrence of fixed-pattern noise is suppressed.

Furthermore, as shown in FIG. 14D-3, it does not matter that separationparts are omitted at some branch points, and replaced with the dummytransistor DMT.

In this example, the dummy transistors DMT are arranged instead of thesecond separation parts 140-1 and 140-2.

FIGS. 15A and 15B are diagrams showing an example in which elements arearranged so that switches of separation parts at branch points and dummytransistors hold periodicity.

FIGS. 15A and 15B are circuit diagrams corresponding to FIG. 14D-3, andthe elements are arranged therein so that the switches of the separationparts at the branch points and the dummy transistors hold periodicity.

The dummy transistor DMT of FIG. 15B is configured such that, as anexample, the gates, the drains, and the sources of two NMOS transistorsNT1 and NT2 which form the switch of the separation part and arecascade-connected to each other are grounded.

FIG. 16 is a diagram showing an example in which the elements arearranged so that the switches of the separation parts at the branchpoints and the dummy transistors hold periodicity and the dummytransistors have a predetermined function.

As shown in FIG. 16, the dummy transistor DMT can be configured to haveany function.

In the example of FIG. 16, the dummy transistor DMT is caused tofunction as a constant current source I1 of a source follower.

Specifically, the source of the NMOS transistor NT1 is grounded, thedrain of the NMOS transistor NT2 is connected to the output signal line116, and the gates of both NMOS transistors NT1 and NT2 are connected tothe power supply for the bias voltage Vb to constitute the constantcurrent source I1.

FIG. 17 is a diagram showing a layout example when a 4×4 pixel cellsshare the stack-connecting terminal.

When the 4×4 pixel cells share the stack-connecting terminal 118, asshown in FIG. 17, for example, it is possible to arrange the separationpart 140 in a gap between the pixel cells 110A.

Particularly, it is possible to arrange a separation part withoutreducing the area of a light sensing part in a rear surface irradiationtype image sensor in which photoelectric conversion is performed byirradiating a surface opposite to a transistor-arranged surface withlight, or an image sensor in which a photoelectric conversion film isformed upper than a wiring layer.

7. Fifth Embodiment

FIG. 18 is a diagram showing a stacking structure example of a firstsemiconductor layer and the second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a fifth embodiment ofthe technology.

In the first semiconductor layer 200, a wiring layer 202 is formed on asilicon (Si) substrate (p-well) 201.

An n-type diffusion region 2011 is formed on the Si substrate 201 as aphotoelectric conversion unit (PD) 111, and a p+ type diffusion region2012 is formed over the surface part of the photoelectric conversionunit 111 (the boundary between the wiring layer 202).

n+ diffusion regions 2013 of FDs and n+ diffusion regions 2014 of thetransistors for the switches of the separation parts 140 are formed inplural over the surface part in the Si substrate 201.

In the wiring layer 202, a gate wiring 2021 and a signal propagationwiring 2022 of each transistor are formed in an insulating layer such asSiO₂, and a micro-pad 2023 formed of Cu, or the like is formed over thesurface part thereof.

In addition, a via (VIA) 2024 is formed in the wiring layer 202 in orderto connect a n+ diffusion region 2014 of the separation part 140 to themicro-pad 2023.

In the second semiconductor layer 210, a wiring layer 212 is formed on aSi substrate 211.

Diffusion regions 2111 and 2112 of transistors are formed in the surfacepart on the Si substrate 211.

In the wiring layer 212, a gate wiring 2121 and a signal propagationwiring 2122 of each transistor are formed in an insulating layer such asSiO₂, and a micro-pad 2123 formed of Cu, or the like is formed over thesurface part thereof.

In addition, a via (VIA) 2124 is formed in the wiring layer 212 in orderto connect a diffusion region 2111 and the like to a micro-pad 2123.

A CMOS image sensor (solid-state imaging element) 100E of FIG. 18 is animage sensor in which the photoelectric conversion unit 111 is formed onthe semiconductor face opposite to the transistors and the wiring layersand the rear surface is irradiated with light, using a micro-bump BMP asthe stack-connecting terminal 118.

In the image sensor 100E, the surface part of the wiring layer 202 ofthe first semiconductor layer 200 and the surface part of the wiringlayer 212 of the second semiconductor part 210 are opposed to each otherto connect the micro-pad 2023 and the micro-pad 2123 with the micro-bumpBMP.

8. Sixth Embodiment

FIG. 19 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a sixth embodiment ofthe technology.

A point that an image sensor 100F according to the sixth embodimentdiffers from the image sensor 100E according to the fifth embodiment isthat the micro-pad 2023 and the micro-pad 2123 as the uppermost wiringare connected to each other without using a micro-bump.

9. Seventh Embodiment

FIG. 20 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a seventh embodimentof the technology.

Point that an image sensor 100G according to the seventh embodimentdiffers from the image sensor 100F according to the sixth embodiment areas follows.

In the image sensor 1000, the Si substrate 211 of the secondsemiconductor layer 210 is arranged in the surface side of the wiring202 of the first semiconductor layer 200.

In addition, the micro-pad 2123 of the wiring layer 212 of the secondsemiconductor layer 210 is connected to the micro-pad 2023 of the wiringlayer 202 of the first semiconductor layer 200 by a through hole VIAelectrode 213 that penetrates the second semiconductor layer 210.

Furthermore, the wiring 2122 of the wiring layer 212 of the secondsemiconductor layer 210 is connected to the wiring 2022 of the wiringlayer 202 of the first semiconductor layer 200 by a through hole VIAelectrode 214 that penetrates the second semiconductor layer 210.

10. Eighth Embodiment

FIG. 21 is a diagram showing a stacking structure example of a firstsemiconductor layer, a second semiconductor layer, and a thirdsemiconductor layer of a CMOS image sensor (solid-state imaging element)according to an eighth embodiment of the technology.

The CMOS image sensor 100H according to the eighth embodiment has astacking structure of the first semiconductor layer 200, the secondsemiconductor layer 210, and a third semiconductor layer 230.

In the third semiconductor layer 230, a wiring layer 222 is formed on aSi substrate 221.

On the Si substrate 221, diffusion regions 2211 and 2212 of transistorsare formed in the surface part.

In the wiring layer 222, a gate wiring 2221 and a signal propagationwiring 2222 of each transistor are formed in an insulating layer such asSiO₂, and a micro-pad 2223 formed of Cu, or the like is formed over thesurface part thereof.

In addition, a via (VIA) 2224 is formed in the wiring layer 222 in orderto connect the diffusion region 2211 and the wiring 2222 or the wiring2222 and the micro-pad 2223.

In the image sensor 100H, a photoelectric conversion film 240 is formedon the wiring layer 202 of the first semiconductor layer 200, and thewiring 2022 of the first semiconductor layer 200 and the wiring 2122 ofthe second semiconductor layer 210 are connected by a through hole VIA203 which penetrates the first semiconductor layer 200.

In addition, the micro-pad 2123 of the wiring layer 212 of the secondsemiconductor layer 210 and the micro-pad 2223 of the wiring layer 222of the third semiconductor layer 220 are connected by a through hole VIAelectrode 213H which penetrates the second semiconductor layer 210.

Furthermore, as a photoelectric conversion film on the wiring layer, anorganic photoelectric conversion film is well known. In addition, thesemiconductor layer may be stacked with any number of layers.

As such, if a photoelectric conversion layer is formed on a layerdifferent from the transistors within the first semiconductor layer 200,it is possible to arrange separation means and stack-connectingterminals with a high degree of freedom without reducing the area oflight sensing elements.

In addition, it is possible to stack signal processing circuits ormemory circuits as a semiconductor layer of the third semiconductorlayer and to be connected by the stack-connecting terminal 118.

11. Ninth Embodiment

FIG. 22 is a diagram showing a stacking structure example of a firstsemiconductor layer and a second semiconductor layer of a CMOS imagesensor (solid-state imaging element) according to a ninth embodiment ofthe technology.

In the CMOS image sensor 100I according to the ninth embodiment, thefirst semiconductor layer 200 is formed in the same layout as in FIG.13, and the second semiconductor layer 210 is formed with an ADconversion unit 150 and a signal processing unit 160.

In the example of FIG. 22, one signal processing unit 160 is arranged inthe center part, and respective two AD conversion units 150 are arrangedin both sides of long edge parts.

In addition, in the CMOS image sensor 100I, AD conversion circuits 151,152, 153, and 154 are arranged in respectively parallel with eachstack-connecting terminal 118.

Furthermore, if the pixel cells have amplifying circuits for signaloutput, a pixel sharing type in which a plurality of light sensingelements shares the amplifying circuits, a pixel configuration in whicha charge holding region that realizes batch exposure is provided in apixel, or the like is also acceptable.

As described above, it is possible to obtain the following effectsaccording to the technology.

In an image sensor in which a connecting terminal that is connected to astacked (three-dimensionally mounted) different semiconductor layer isshared in an amplifying circuit of a plurality of pixel cells, it ispossible to reduce parasitic capacitance of an output signal line andrealize speed-up and low power consumption of reading out of outputsignals from the pixels.

In addition, since the above effect can be realized only with simpleaddition of switch circuits and wiring, almost no influence is given tothe reduction of light sensing elements or deterioration in resolutionin a rear surface irradiation image sensor or an image sensor using anorganic photoelectric conversion film.

By arranging a stack-connecting terminal and a separation part at abranch point in the vicinity of the center of a pixel group connectedthereto, there are effects of speed-up and low power consumption byminimized parasitic capacitance and of reducing the range of an inputvoltage necessary for an analog signal processing circuit of the latterstage by uniform wiring resistance.

A solid-state imaging element that brings the above effects can beapplied as an imaging device of a digital camera or a video camera.

12. Tenth Embodiment

FIG. 23 is a diagram showing an example of a configuration of a camerasystem to which the solid-state imaging elements according to theembodiments of the technology are applied.

The camera system 300 is provided with an imaging device 310 to whichone of the CMOS image sensors (solid-state imaging elements) 100 and100A to 100I according to the embodiments is applicable, as shown inFIG. 23.

Furthermore, the camera system 300 includes an optical system that leadsincident light to a pixel region of the imaging device 310 (forms theimage of a subject), for example, a lens 320 that forms an image on animaging plane with the incident light (image light).

The camera system 300 includes a driving circuit (DRV) 330 which drivesthe imaging device 310 and a signal processing circuit (PRC) 340 whichprocesses output signals of the imaging device 310.

The driving circuit 330 has a timing generator (not shown in thedrawing) which generates various timing signals including start pulsesand clock pulses that drive circuits in the imaging device 310 anddrives the imaging device 310 with a predetermined time signal.

In addition, the signal processing circuit 340 performs a predeterminedsignal process for output signals of the imaging device 310.

The image signals processed in the signal processing circuit 340 arerecorded on a recording medium, for example, a memory, or the like.Image information recorded on the recording medium is made into hardcopy by a printer, or the like. In addition, the image signals processedin the signal processing circuit 340 are displayed as moving images on amonitor including a liquid crystal display or the like.

As described above, it is possible to realize a camera with highprecision and low power consumption by mounting the above-describedimaging elements 100 and 100A to 100I in an imaging device including adigital still camera, or the like as the imaging device 310.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-197734 filed in theJapan Patent Office on Sep. 3, 2010, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An apparatus comprising: a solid-state imagingelement; an optical system which forms an image of a subject on thesolid-state imaging element; and a signal processing circuit whichprocesses an output image signal of the solid-state imaging element,wherein, the solid-state imaging element includes (a) a firstsemiconductor layer including (i) a pixel array part having a pluralityof pixel cells in a two-dimensional array, each of the pixel cellshaving a photoelectric conversion part and an amplifying circuit in aone-to-one relationship, and (ii) an output signal line configured toreceive signals from a plurality of the amplifying circuits; (b) asecond semiconductor layer stacked on the first semiconductor layer; and(c) a plurality of stack-connecting parts electrically connecting thefirst and second semiconductor layers, the plurality of pixel cellsinclude a first set of pixel cells and a second set of pixel cells, theoutput signal line includes a first signal line and a second signalline, the first set of pixel cells share the first signal line and thesecond set of pixel cells share the second signal line in a columndirection, respectively, and the first and second signal lines areconfigured to be selectively connected and selectively disconnected toat least one of the stack connecting parts by a switch located betweenthe output signal line and at least one of the stack connecting parts,the switch being located between predetermined neighboring pixel cells.2. The apparatus of claim 1, wherein: the plurality of pixel cellscomprise a pixel group, and the at least one stack-connecting part isarranged in a vicinity of a center of the pixel group sharing the outputsignal line connected to the at least one stack-connecting part.
 3. Theapparatus of claim 1, wherein: the plurality of pixel cells comprise apixel group, and the switch is arranged in a vicinity of a center of thepixel group.
 4. The apparatus of claim 1, further comprising dummyelements that are not connected to the output signal line and arearranged in the two-dimensional array of the pixel cells in the pixelarray part.
 5. The apparatus of claim 4, wherein the dummy elements arearranged so that two-dimensional arrangement of the switch is periodic.6. The apparatus of claim 1, further comprising: a pixel driving partconfigured to drive the pixel cells of the pixel array part arranged onthe first semiconductor layer, wherein, the pixel group sharing the atleast one stack-connecting part is in a two-dimensional array of whichrows and columns have two or more pixels, and the output signal lineconnected to the plurality of amplifying circuits of the pixel cellsselected simultaneously in parallel by the pixel driving part isconnected to the stack-connecting part through the switch.
 7. Theapparatus of claim 1, wherein, each photoelectric conversion part isconnected to a respective amplifying circuit, each amplifying circuitincluding an amplifying transistor and a selection transistor.
 8. Theapparatus of claim 7, wherein: each amplifying transistor has (a) a gateterminal configured to receive signals obtained from at least one of thephotoelectric conversion parts, (b) a drain terminal connected to apower supply, and (c) a source terminal connected to the output signalline, and a constant current source arranged on a first semiconductorlayer side or a second semiconductor side is connected to the outputsignal line.
 9. The apparatus of claim 8, wherein each source terminalof a respective amplifying transistor is connected to the output signalline through a respective selection transistor.
 10. The apparatus ofclaim 1, wherein the first semiconductor layer includes a light sensingelement that can sense light radiated from a face opposed to a facewhere transistors and wiring layers are formed.
 11. The apparatus ofclaim 1, wherein the first semiconductor layer includes a wiring layer,and a photoelectric conversion film as a light sensing element formed onthe wiring layer.
 12. The apparatus of claim 1, wherein each of thestack-connecting parts include a terminal with which a first micro-padarranged on an outermost layer of the first semiconductor layer and asecond micro-pad arranged on an outermost layer of the secondsemiconductor layer, the second micro-pad being at a positioncorresponding to the first micro-pad and being connected to the firstmicro-pad through a micro-bump.
 13. The apparatus of claim 1, whereineach of the stack-connecting parts include a terminal with which a firstmicro-pad arranged on the outermost layer of the first semiconductorlayer and a second micro-pad arranged on the outermost layer of thesecond semiconductor layer, the second micro-pad being at a positioncorresponding to the first micro-pad and being directly pasted to thesecond micro-pad.
 14. The apparatus of claim 1, wherein each of thestack-connecting parts include a contact via penetrating a semiconductorlayer or an insulating layer of both or either of the firstsemiconductor layer or the second semiconductor layer.
 15. The apparatusof claim 1, wherein the second semiconductor layer includes a pluralityof analog and digital (AD) conversion units.
 16. The apparatus of claim15, wherein the plurality of AD conversion units is arranged so as to bein parallel with each of the stack-connecting parts.
 17. The apparatusof claim 1, further comprising at least one of a signal processingcircuit and a memory circuit on a third semiconductor layer or asemiconductor layer stacked as a succeeding semiconductor layer andconnected by the stack-connecting parts.
 18. The apparatus of claim 1,wherein at least one of the plurality of stack-connecting parts includesa first micro-pad on the first semiconductor layer and a secondmicro-pad on the second semiconductor layer, the first and secondmicro-pads being in direct contact with each other.
 19. The apparatus ofclaim 1, wherein at least one of the plurality of stack-connecting partsincludes a first wiring layer formed in the first semiconductor layerand a second wiring layer formed in the second semiconductor layer, thefirst and second wiring layers being connected through a through holevia electrode.
 20. The apparatus of claim 19, wherein at least one ofthe plurality of stack-connecting parts further includes a third wiringlayer formed in the first semiconductor layer and a fourth wiring layerformed in the second semiconductor layer, the first and second wiringlayers being connected through a through hole via electrode.
 21. Theapparatus of claim 4, wherein the dummy elements are dummy transistors22. The apparatus of claim 21, wherein the dummy transistors function asa constant current source of a source follower.